Evapotranspiration of Mature Orange Trees Under Drip Irrigation in an Arid Climate

ABSTRACT EVAPOTRANSPIRATION (ET) of mature Valencia orange trees (Citrus sinensis L.) was determined from a large field experiment in southwest Arizona. ET was calculated as the difference between accurate measure-ments of the amount of water applied (rainfall included) and drainage below the root zone. The amount of drain-age was estimated from various techniques of calculating leaching fraction based on the ratios of total salt and chloride concentrations. In a climate where the annual pan evaporation is 2520 mm, ET was 1470 mm or about 50 m3 per tree. The daily rate of ET, averaged by month, ranged from a low of 0.8 mm in December to 7.5 mm in August. Sev-eral predictive equations for ET were in close agreement with these values.